1. Technical Field
This disclosure relates to an optical device, a laser apparatus including the optical device, and an extreme ultraviolet (EUV) light generation system including the laser apparatus.
2. Related Art
In recent years, semiconductor production processes have become capable of producing semiconductor devices with increasingly fine feature sizes, as photolithography has been making rapid progress toward finer fabrication. In the next generation of semiconductor production processes, microfabrication with feature sizes at 60 nm to 45 nm, and further, microfabrication with feature sizes of 32 nm or less will be required. In order to meet the demand for microfabrication at 32 nm or less, for example, an exposure apparatus is expected to be developed, in which an apparatus for generating extreme ultraviolet (EUV) light, at a wavelength of approximately 13 nm is combined with a reduced projection reflective optical system.
Three kinds of apparatuses for generating EUV light have been known in general, which include an LPP (Laser Produced Plasma) type apparatus in which plasma generated by irradiating a target material with a laser beam is used, a DPP (Discharge Produced Plasma) type apparatus in which plasma generated by electric discharge is used, and an SR (synchrotron radiation) type apparatus in which orbital radiation is used.